When a silver halide light-sensitive material is processed with a developing solution which contains a compound capable of dissolving silver halides, e.g., thiosulfates and sulfites, elution of a good deal of silver complexes from the sensitive material into the developing solution takes place. The silver complexes eluted into the developing solution are reduced with the developing agent and converted to fine metallic silver, resulting in the generation of silver sludge in the developing solution.
A developing solution which contains sulfite in a high concentration, especially in a concentration of about 0.1 mole/1 or above, has excellent quality in maintaining its developing activity upon storage. However, having once used, the developing solution tends to be contaminated and to cause developing-stain on surfaces of sensitive materials developed. This phenomenon turns out to be a serious disadvantage, especially in the case of high temperature development carried out using an automatic developing processor. This is because when development-processing is carried out using an automatic developing processor not only is silver sludge suspended in the developing solution but also silver particles adhere to walls of the processing tank and to rollers of the developing processor and thereby, sensitive materials are subject to contamination with silver deposited thereon in a form of roller streaks, the so-called silver stain, which silver turns yellow or brown by reflecting light therefrom. Silver stain is generated on the surface of a sensitive material equally, regardless of the quantity of light to which the sensitive material is exposed, and forms a colored layer on the surface resulting in a marked deterioration of image quality obtained. Namely, silver stain spoils directly the quality of the photographic image. Therefore, when photographic light-sensitive materials are processed with such a developing solution as described above using an automatic developing processor, the qualities of finished photographs are spoiled to a great extent.
As an inhibitor of silver sludge or liquid contamination, 2-mercapto-1,3,4-thiadiazoles (as described in British Pat. No. 940,169), 2-mercapto-1,3,4-oxadiazoles of 1-phenyl-5-mercaptotetrazole (as described in U.S. Pat. No. 3,173,789), D,L-6,8-dithiooctanoic acid (as described in U.S. Pat. No. 3,318,701), o-mercaptobenzoic acid (as described in British Pat. No. 1,144,481), aliphatic mercaptocarboxylic acids (as described in U.S. Pat. No. 3,628,955), L-thiazolidine-4-carboxylic acid (as described in J. Photogr. Sci., volume 13, page 233 (1965)), disulfide compounds (as described in Japanese Patent Application (OPI) 36029/'77), 2-benzoxazolethiol and 2-benzimidazolethiol (as described in Photogr. Sci. Eng., volume 20, page 220 (1976)), and so on are known.
However, none of the above-described compounds, in a photographic developing solution which is capable of dissolving silver halide, especially in a developing solution containing sulfite in a high concentration, functions as a sludge inhibitor effectively enough to provide satisfaction. For instance, aliphatic mercaptocarboxylic acid compounds are air oxidized and consequently, they tend to be oxidized in the air and lose rapidly their sludge preventing effects. In addition, some of these compounds have unpleasant odors. The use of 1-phenyl-5-mercaptotetrazole or 2-benzoxazolethiol in a large amount can reduce liquid contamination in some cases. However, in other cases these compounds react with silver ion to produce slightly soluble silver salts in the developing solutions and thereby, films are rather stained, rather than prevented silver stain. In addition, a large amount of such a compound in a developing solution disturbs the ability to achieve satisfactory photographic characteristics.
On the other hand, high temperature development, especially high temperature rapid processing using an automatic developing processor, is known as a process for carrying out development efficiently, and has proved fruitful upon the application to the processings of various kinds of sensitive materials. However, since sensitive materials are processed at high temperatures in this process, emulsion films under processing must be previously prevented from becoming brittle at high temperatures so as to have sufficient mechanical strength to withstand the stress applied thereto by rollers and belts of the automatic developing processor. Therefore, it is necessary to devise a technique to increase the mechanical strength of an emulsion film as the development in a developing solution progresses and further, may be kept there during the processing. For this purpose, the processing is carried out using a developing solution to which an aldehyde series hardener is added. According to this process, the total processing time can be shortened due to the processing at a high temperature, and the object of speeding up the processing can be attained so far as it goes. However, the development-processing with, e.g., developing solutions containing aldehydes, especially aliphatic dialdehydes, is attended by a marked generation of fog. The higher the temperature of the developing solution used is, and the longer the period of using the developing solution is, the more remarkable the tendency for the developing solution to cause fog becomes The occurrence of such fog resulting from aldehydes can be prevented by the use of a powerful fog restrainer, such as benzotriazole or 1-phenyl-5-mercaptotetrazole (which are described in L. F. A. Mason, Photographic Processing Chemistry, page 40 by THE FOCALPRESS, 1966) so far as it is concerned. On the other hand, the addition of such powerful fog restrainers to a developing solution retards the development to a great extent and thereby, the sensitivities of emulsions are reduced sharply.
5-Nitroindazole described in British Pat. No. 1,269,268 acts as an effective antifoggant in a developing solution containing an aldehyde series hardener, while it has the disadvantages that an appropriate solvent is required because of its poor solubility in a developing solution and its stability in a developing solution after the lapse of a long time is low.
Furthermore, satisfactory effect as a silver sludge inhibitor also is not exhibited.